Use of a Piston in the Car - Coursework Example

Assignment: Engineering Report To write a report on the use of a piston in the car Student’s Name: Course Code: Date of Submission: Executive Summary This report discusses the roles played by an engine piston in a car. It elaborates on the role of the piston during the intake stroke where its movement brings about the opening of the inlet valve at the same time creating a vacuum within the cylinder. The piston also participates in the compression stroke where its upward movement compresses the air/air-fuel mixture to attain the required compression ratio. In the power stroke the piston converts the produced energy into the right form of energy and transmits it to the crankshaft and flywheel and other targets. In the exhaust stroke the piston ensures that the burned gases are eliminated from the cylinder. The piston also makes sure that the contents of the combustion chamber do not leak into the sump. The piston also plays a role of regulating the temperatures within the cylinder. Table of Contents Executive Summary 2 Table of Contents 3 Introduction 4 Car Piston 5 What a Car Piston can do in the cylinder 5 The Piston and the Intake stroke 6 The Piston and the Compression stroke 6 The Piston and the Power stroke 7 The piston and the Exhaust stroke 7 The piston and other related functions 8 Conclusion 9 References 10 Introduction Pistons are made up aluminium alloys and are very important components of a car engine because they are the car’s main driving force. Their movements up and down the cylinder result in the generation of power that propels the car (Linde 2011). Thus, a piston is a piece of metal cylindrically shaped that undergoes the up and down movements within an engine cylinder (Brain 2000). Its rotatory motion is transferred to the crankshaft making it to rotate as well. It also makes it possible for oxygen to get into the combustion chamber and exhaust gases to leave the combustion chamber (Linde 2011). The piston within a car achieves this by undergoing four strokes to complete one operating cycle hence the name four stroke cycle engines. This report looks at the functions of a piston within a cylinder. Figure 1-illustaration: pistons in cylinders courtesy auto.howstuffworks.com/engine2.htm Car Piston What a Car Piston can do in the cylinder The enclosed space between the top end of the cylinder and the piston is called the combustion chamber. This is where the piston operates. The chamber is sealed by two valves; the inlet valve and the exhaust valve. And at the bottom of the piston is the connecting rod which connects the piston to the crankshaft and the crankshaft is connected to the drive wheels of the car. So whenever the piston and connecting union go up and down the cylinder they make the crankshaft to rotate and so does the drive wheels (Linde 2011; Todd 1999; Abdo 2011). The movements of the piston are called strokes and the piston undergoes four strokes to complete one cycle that generates the power that drives the engine hence the name four stroke cycle engine. In each stroke, the piston achieves different functions. These strokes include the intake stroke, the compression stroke, the power stroke and the exhaust stroke (Todd 1999). Figure 2-piston and associated parts courtesy of www.substech.com The Piston and the Intake stroke At the onset of this stroke the piston is located at the top of the cylinder otherwise commonly referred to as the top dead centre. During this stroke the piston moves down from the top dead centre of the cylinder to the bottom dead centre of the cylinder. This movement makes various activities within the cylinder possible. First it increases the volume of the cylinder and at the same time lowering the pressure within the cylinder. This is effected by the creation of a vacuum inside the cylinder. The second function that this movement of the piston achieves is, it causes the inlet valve to open. This opening of the inlet valve allows air or air-fuel mixture to rush in into the cylinder to fill the vacuum created in the cylinder by the downward movement of the piston (Linde 2011; Todd 1999; Abdo 2011). The Piston and the Compression stroke During this stroke the inlet valve that was open in the previous stroke closes. The closing of the inlet valve is achieved by the movement of the cylinder up the cylinder from the bottom dead centre towards the top dead centre of the cylinder. The upward movement of the piston not only makes the inlet valve to close but also does the compression function. Its upward movement also compresses the air or the air-fuel mixture in the combustion chamber. And in so doing it increases the pressure within the combustion chamber by increasing the compression ratio. This is in order to make the subsequent explosion more powerful. At this position of the piston the crankshaft has achieved a one full rotation so half of the cycle has been completed but power is yet to be produced. During the power production phase the piston also comes in hand in making sure the produced power gets to the intended targets (Linde 2011; Todd 1999; Abdo 2011; Brain 2000). The Piston and the Power stroke This stroke is also known as the combustion stroke because it is at this stroke that the air and fuel mixture are ignited. The fuel-air mixture is burned to produce power hence the name power stroke. Here the piston has reached it top most position within the cylinder and it has compressed the air or air-fuel mixture to the required compression ratio. In petrol using engines at this point a spark is introduced by the spark plug into the highly compressed air-fuel mixture and mixture ignites and burns violently. In diesel using engines at this point the air has been highly compressed and is steaming hot and at this level of hotness is when the fuel injector injects diesel fuel into the combustion chamber in form of mists. Because of the hotness of the air the injected diesel fuel explodes into flames and burns violently. With the inlet and exhaust valves closed, the burning air-fuel mixture produces heat and pressure energies within the cylinder. This moves the piston down the cylinder. This movement aspect of the piston converts these energies into mechanical energy which is transferred from the piston to the crankshaft via the connecting rod. The crankshaft converts this linear motion into rotatory motion enabling us to steer our cars to whatever direction. Thus the piston also plays a role of transmitting the produced energy leave alone converting it into the right form of energy to bring about movement of the car (Linde 2011; Todd 1999; Abdo 2011). At the end of this phase the piston is at the bottom dead centre of the cylinder. The piston and the Exhaust stroke After the burning of the air-fuel mixture within the combustion chamber burned gases are produced which need to be eliminated from the combustion chamber before another cycle commences. To achieve this, the piston moves upwards and this open the exhaust valve allowing the burned gases into the exhaust manifold from which they are eliminated through the exhaust system and out into the environment (Linde 2011; Todd 1999; Abdo 2011). Most cars have four cylinders in their engines and so four pistons. The cylinders do not go on at the same time, they follow a particular order called the firing order in that that cylinders happen to be at different strokes at the same time to ensure continuous supply of power to the engine (Todd 1999). Figure 3-illustration of the four strokes-www.substech.com The piston and other related functions The piston has piston rings on its surface which also play very important roles within the cylinder. The upper two rings known as the compression rings closes the piston clearance gap that is the gap between the cylinder wall and the piston. This ensures that pressure does not escape from the combustion chamber into the oil containing sump. The lower ring also called the oil ring ensures that the walls of the cylinder are always coated with oil film to prevent wear as a result of friction. The piston also plays a role of dissipating heat. The shape of the piston crown, that is irregular with projecting surfaces helps and dissipate heat. The oil ring also has a cooling aspect inside the cylinder (Linde 2011). Conclusion In conclusion, as per the report the piston is a very vital component of a car engine as it is the driving force behind every functioning engine. Whenever the engine is running so is the piston making sure that it plays a role in the production of power within the engine. It does not stop there because the piton goes ahead in ensuring that the produced power is transmitted to places where it is required. The piston also takes part in the process of making sure that the by-products of the power producing process within the cylinder are eliminated from the cylinder. The four strokes of the piston take place very quickly and repeat continuously to ensure a continuous supply of power to the engine. All those four basic strokes must take place for the correct running of the engine. References Abdo, A 2011, Power Equipment Engine Technology, Cengage Learning, New York. Brain, M 2000, How Car Engine Works, viewed 20 March 2015, http://auto.howstuffworks.com/engine1.htm Linde, A 2011, How your Car Works: Your guide to the Components and Systems to Modern Cars including hybrid and electric vehicles, Veloce Publishing, Dorset, England. Todd, J 1999, Auto Repair for DUMMIES, Hungry Minds Inc., New York. Read More